Meeting Abstract
P2.142 Tuesday, Jan. 5 Homology model of Fundulus heteroclitus calsequestrin reveals structural differences that may contribute to thermal adaptation of F. heteroclitus NIENOW, T.E.*; WHITTINGTON, A.C.; GROVE, T.J.; Valdosta State University; Florida State University; Valdosta State University tjgrove@valdosta.edu
Calsequestrin (CSQ) is an acidic calcium-binding protein in the sarcoplasmic reticulum. Calcium stabilizes three thioredoxin-like domains within CSQ and causes dimerization and polymerization at higher calcium concentrations. While CSQ structure and function have been studied in mammals, the temperature dependence of CSQ in poikilothermic teleosts has yet to be explored. To investigate the structural basis of thermal adaptation of CSQ, we determined the full length cDNA sequence of skeletal muscle CSQ from F. heteroclitus, a small intertidal fish adapted to dramatic seasonal and tidal temperature changes. Using the deduced amino acid sequence we created a homology model based on the crystal structure of rabbit skeletal CSQ (1A8Y). F. heteroclitus and rabbit CSQs share 67% identity, indicating that rabbit CSQ crystal structure provides a good template above the “twilight zone” threshold. Excluding the signal sequence and negatively charged tail, F. heteroclitus CSQ has fewer acidic residues (79) and more basic residues (38) than rabbit CSQ (87 acidic, 30 basic), leading to an overall smaller negative charge on F. heteroclitus CSQ. Interestingly, the acidic tail in F. heteroclitus CSQ is longer than in rabbit, which gives fish CSQ a larger negative charge at pH 7 (-97.6 and -65.5, respectively). Additionally, F. heteroclitus CSQ has more aromatic residues buried in the interior of the protein, including five conserved tryptophans in the third domain. Continued investigation of the effects these differences have on non-covalent interactions within the tertiary structure may reveal the molecular basis for adaptation of F. heteroclitus in the face of an unstable thermal environment. Supported by NSF IOS-0817805.
